Light source apparatus provided with beam shaping element and optical pick-up apparatus having the same

ABSTRACT

The present invention has a beam shaping element for converting the light source 11 into a light flux whose emitting angle is almost equal and for projecting it, and a generation amount of the astigmatism generated by the temperature change is suppressed by a linear expansion of the beam shaping element.

FIELD OF THE INVENTION

The present invention relates to a light source apparatus and an opticalpick-up apparatus, which are provided with a beam shaping element.

BACKGROUND OF THE INVENTION

Generally, for the optical pick-up apparatus, a semiconductor laser suchas LD (laser diode) is used as the light source. Because a diverginglight flux projected from the semiconductor laser has an ellipticalcross sectional shape (that is, a distribution of the light emittingstrength is elliptical), it is necessary that the elliptical light fluxfrom the semiconductor laser is converted to a circular light flux and alight utilization efficiency is increased.

As a beam shaping element (beam-shaper) to shape the sectional shape ofthe light flux from an elliptic to a circle, an optical element whoseoptical surface is an anamorphic surface or cylindrial surface, is wellknown. (For example, refer to Patent Documents 1 and 2).

(Patent Document 1) Tokkai No. 2003-178480

(Patent Document 2) Tokkai No. 2003-188452

(Patent Document 3) Tokkai No. 2002-323673

Recently, there are many cases where, in the optical pick-up apparatus,a light flux of short wavelength or a light flux of a large power isused. Therefore, there is a problem that a change of environmentaltemperature brings a change of performance (refractive index or shape)of an optical element composing an optical system or a change of awavelength of a projected light flux from the semiconductor laser, andthe astigmatism is generated. Accordingly, in order to suppress thechange of the lens characteristic following a change of such aenvironmental temperature, generally, there are many cases where theoptical element made of glass is used, and the optical element made ofglass is adopted also for the beam-shaper disclosed in the PatentDocuments 1 and 2. On the one hand, in the Patent Document 3, it iswritten that the beam-shaper made of plastic whose aberration change issmall, is used.

When plastic is used, the performance change due to the temperaturechange is larger than glass. Also in Patent Document 3, a problem thatthe astigmatism is generated due to the temperature change by using theplastic shaping element is written, and it is written that theastigmatism is suppressed by the linear expansion of the plastic-madelens barrel provided between the light source and the beam-shaper.

However, in a method of the Document 3, because the linear expansion ofthe lens barrel provided between the light source and the beam-shaper isused for the astigmatism suppression, it is necessary to payconsideration for the selection of the material constituting the lensbarrel for appropriately suppressing the astigmatism, or there are manylimitations to the design work also for the thickness of the lens barrelitself or the length, and as a whole, there is a problem that the degreeof freedom of the manufacture becomes narrow. Accordingly, specially,even when the element made of plastic is used, a result is brought aboutin which a merit of low cost•small size•light weight can not be fullyexhibited.

Furthermore, in the case of the beam-shaper of the Document 3, becauseboth of an incident surface and an outgoing surface are composed of atoric surface, the surface shape becomes complicated, as a result, a lowcost element, apparatus can not be realized.

An object of the present invention considers the above problems and isto provide a beam-shaper, light source apparatus, and optical pick-upapparatus, which are excellent in a point of low cost, small size, lightweight, by which, while various aberrations including the generation ofthe astigmatism following the change of environmental temperature areeffectively suppressed, the divergent light flux whose sectional shapeis almost circular, can be projected.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the above problems. Inorder to solve the above problems, the present invention ischaracterized in that: it has, as the first structure, a light sourcewhich projects the light flux whose emission angle is different in thehorizontal direction and in the vertical direction, and a beam-shaper ofa single lens formed of plastic for converting the light flux into thelight flux whose emission angle is almost equal, and for projecting it,whose linear expansion coefficient α_(n) satisfies the followingconditional expression (1),5.0×10⁻⁵<α_(n)<8.0×10⁻⁵  (1)and a part of the beam-shaper is a light source apparatus fixed to thelight source so that the astigmatism generated following the refractiveindex change of the beam-shaper generated due to the temperature changeis suppressed by the interval change between the light source and theincident surface of the beam-shaper, which is generated by the linearexpansion of the beam-shaper.

Further, as the second structure, the present invention is characterizedin that: the beam-shaper is fixed so that the outgoing surface is notpractically changed in the optical axis direction to the light source.

Further, as the third structure, it is characterized in that: thebeam-shaper is structured in such a manner that it suppresses theastigmatism generated due to the temperature change by using theastigmatism generated following the shape change due to the temperaturechange of the beam-shaper.

Further, as the fourth structure, it is characterized in that: a fixingmember to fix the beam-shaper outgoing surface is made of a materialwhose linear expansion coefficient satisfies 1.0×10⁻⁵<α_(n)<3.0×10⁻⁵.Further, as the fifth structure, in the incident surface and outgoingsurface of the beam-shaper, the sectional shape of the horizontaldirection or vertical direction of at least one optical surface isnon-circular arc.

Further, as the sixth structure, it is characterized in that: thesurface shape of the beam-shaper incident surface satisfies thefollowing Math-1 or Math-2.

$\begin{matrix}{{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{R_{y}\left( {1 + \sqrt{\left. {1 - {\left( {1 + k_{y}} \right){Y^{2}/R_{y}^{2}}}} \right)}} \right.} + {\sum\limits_{i}{A_{yi}Y^{i}}}} \right)^{2}} & \left\lbrack {{Math}\text{-}1} \right\rbrack \\{{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = \left( {R_{y} - \frac{X^{2}}{R_{x}\left( {1 + \sqrt{\left. {1 - {\left( {1 + k_{x}} \right){X^{2}/R_{x}^{2}}}} \right)}} \right.} + {\sum{A_{xi}X^{i}}}} \right)} & \left\lbrack {{Math}\text{-}2} \right\rbrack\end{matrix}$

Hereupon, herein, Z is a distance in the optical axis direction (Z-axisdirection) (an advancing direction of the light is positive), X, Y aredistances in X-axis direction (horizontal direction), Y-axis direction(vertical direction) (height from the optical axis), R_(x)is a paraxialradius of curvature on XZ surface, R_(y) is a paraxial radius ofcurvature on YZ surface, k_(x), k_(y), A_(xi) and A_(yi) arenon-circular arc coefficients.

Further, as the seventh structure, it is characterized in that: thesurface shape of the beam-shaper outgoing surface satisfies thefollowing Math-3 or Math-4.

$\begin{matrix}{{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{\left( {1 + \sqrt{\left. {1 - {Y^{2}/R_{y}^{2}}} \right)}} \right.}} \right)} & \left\lbrack {{Math}\text{-}3} \right\rbrack \\{{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = \left( {R_{y} - \frac{X^{2}}{\left( {1 + \sqrt{\left. {1 - {X^{2}/R_{x}^{2}}} \right)}} \right.}} \right)} & \left\lbrack {{Math}\text{-}4} \right\rbrack\end{matrix}$

Further, as the eighth structure, it is characterized in that: thesurface shape of the beam-shaper outgoing surface satisfies thefollowing Math-1 or math-2.

$\begin{matrix}{{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{R_{y}\left( {1 + \sqrt{\left. {1 - {\left( {1 + k_{y}} \right){Y^{2}/R_{y}^{2}}}} \right)}} \right.} + {\sum\limits_{i}{A_{yi}Y^{i}}}} \right)^{2}} & \left\lbrack {{Math}\text{-}1} \right\rbrack \\{{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = \left( {R_{y} - \frac{X^{2}}{R_{x}\left( {1 + \sqrt{\left. {1 - {\left( {1 + k_{x}} \right){X^{2}/R_{x}^{2}}}} \right)}} \right.} + {\sum{A_{xi}X^{i}}}} \right)} & \left\lbrack {{Math}\text{-}2} \right\rbrack\end{matrix}$

Hereupon, herein, Z is a distance in the optical axis direction (Z-axisdirection) (an advancing direction of the light is positive), X, Y aredistances in X-axis direction (horizontal direction), Y-axis direction(vertical direction) (height from the optical axis), R_(x) is a paraxialradius of curvature on XZ surface, R_(y) is a paraxial radius ofcurvature on YZ surface, k_(x), k_(y), A_(xi) and A_(yi) arenon-circular arc coefficients.

Further, as the ninth structure, it is characterized in that: thesurface shape of the beam-shaper incident surface is a shape whichsatisfies the following Math-3 or Math-4.

$\begin{matrix}{{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{\left( {1 + \sqrt{\left. {1 - {Y^{2}/R_{y}^{2}}} \right)}} \right.}} \right)} & \left\lbrack {{Math}\text{-}3} \right\rbrack \\{{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = \left( {R_{y} - \frac{X^{2}}{\left( {1 + \sqrt{\left. {1 - {X^{2}/R_{x}^{2}}} \right)}} \right.}} \right)} & \left\lbrack {{Math}\text{-}4} \right\rbrack\end{matrix}$

Further, as the tenth structure, it is characterized in that: it has thelight source apparatus and a light converging element forlight-converging the light flux on the information recording surface ofthe optical information recording medium, and provides the opticalpick-up apparatus for conducting the reproducing and/or recording of theinformation on the optical information recording medium.

Further, as the 11-th structure, it is characterized in that: theoptical pick-up apparatus has a light flux conversion element forconverting the light flux projected from the beam-shaper outgoingsurface, and is structured so as to satisfy the following relationalexpression,0.5<(L/S)×fc<1.0.

Hereupon, herein, L is the thickness (mm) on the axis of thebeam-shaper, S is a distance (mm) on the optical axis between the lightsource and the beam-shaper incident surface, and fc is a focal distance(mm) of the light flux conversion element.

According to Table 1(a) and Table 8(a), in the lower limit of the aboveexpression, the astigmatism generated by the change of the refractiveindex due to the temperature change is changed when the thickness on theaxis and the interval between the light source and the beam-shaper arechanged by the temperature change, however, an amount of the changedastigmatism is small, and the astigmatism remains. Further, in the upperlimit of the above expression, the astigmatism generated by the changeof the refractive index due to the temperature change is changed whenthe thickness on the axis and the interval between the light source andthe beam-shaper are changed by the temperature change, however, anamount of the changed astigmatism is excessive, and the astigmatism alsoremains. Therefore, when the range of the above expression is applied,the astigmatism generated at the time of the temperature change can beappropriately suppressed.

Further, as the 12-th structure, it is characterized in that: thedivergent angle conversion element is a coupling lens to convert thelight flux projected from the beam-shaper into the parallel lightparallel to the optical axis. Herein, the linear expansion coefficientα_(n) indicates an average linear expansion coefficient in the normaltemperature range (about −30° C.-70° C.).

Further, “the astigmatism is suppressed” means not only that theastigmatism is made zero, but it is also included that the astigmatismis suppressed to the degree in which, actually, it does not influence onthe recording or reproducing of the information.

Further, “the position in the optical axis direction is not relativelyand practically changed to the light source” means that the distance inthe optical axis direction to the light source is almost constant in therange of change of the environmental temperature.

According to the structure of the present invention, because thegeneration of the astigmatism following the change of the environmentaltemperature is suppressed by the astigmatism generated when thebeam-shaper itself made of plastic is linear-expanded, and the intervalbetween the light source and the element incident surface is changed,the degree of freedom of the material of the member to which thebeam-shaper is attached or dimensions is spread. Further, when a fixingmember for fixing the beam-shaper is structured by a material whoselinear expansion coefficient satisfies 1.0×10⁻⁵<α_(n)<3.0×10⁻⁵, as awhole of the light source apparatus, and optical pick-up apparatus, alow cost, small size, light weight apparatus can be provided.

Further, when the incident surface or outgoing surface as the opticalsurface of the beam-shaper is structured by the surface regulated byMath-1 or Math-2, as compared to a case where the optical surface of thebeam-shaper is structured by a cylindrical surface, not only theastigmatism at the time of temperature change, but the suppression ofthe remained aberration (4thAS (tetraphyllous aberration)) also becomespossible, and the better optical characteristic can be obtained.

Further, when the outgoing surface in addition to the incident surfaceregulated by the above equation is structured by the surface regulatedby Math-3 or Math-4, the better optical characteristic can be obtained.

Further, inversely, when the outgoing surface is structured by thesurface regulated by Math-1 or Math-2, further, also when the incidentsurface is structured by the surface regulated by Math-3 or Math-4, inthe same manner, the better optical characteristic can be obtained.

Further, when both of the incident surface and outgoing surface of thebeam-shaper are structured by surfaces regulated by Math-1 or Math-2, ascompared to a case where the optical surface of the beam-shaper isstructured by a cylindrical surface, not only the astigmatism at thetime of temperature change, but the suppression of the remainedaberration (4thAS (tetraphyllous aberration)) also becomes possible, andthe better optical characteristic can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a structure of an optical pick-upapparatus.

FIG. 2 is a perspective view showing the shape of a beam-shaper.

FIG. 3 is a graph showing the relationship between the remainedaberration to the designed thickness on the axis and the astigmatism atthe time of temperature change.

FIG. 4 is a plan view showing the structure of the optical pick-upapparatus.

FIG. 5( a), FIG. 5( b) are plan views showing a fixed example of thebeam-shaper in the optical pick-up apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, an embodiment to carry out the presentinvention will be detailed below.

In the present embodiment, as shown in FIG. 1, a beam shaping element 20(hereinafter, called also a beam-shaper) according to the presentinvention is applied for an optical pick-up apparatus 10 by which therecording and/or reading of the information is conducted on aninformation recording surface 31 of an information recording medium byusing a laser light (light flux) of a specific wavelength.

The optical pick-up apparatus 10 is generally structured by a laseroscillator 11(light source), beam-shaper 20, coupling lens 12, beamsplitter 13, beam expander 14 (the first beam expander 14 a and thesecond beam expander 14 b), stop 15, objective lens 16 (the firstobjective lens 16 a and the second objective lens 16 b), cylindricallens 17, concave lens 18, and light sensor 19.

The light flux projected from the light source 11 has a differentspreading angle to a direction orthogonal to the optical axis L, and theXY direction (the horizontal direction and the vertical direction)orthogonal to each other.

Then, an XY cross section of this light flux, is about an elliptic shapein which the X direction is a short diameter, and the Y direction is along diameter.

Operations of the optical pick-up apparatus structured as describedabove will be described below.

The light flux projected from the light source 11 is incident on theincident surface of the beam-shaper 20 and projected from the outgoingsurface after the sectional shape of the light flux is shaped. An actionto the light flux by the beam-shaper 20 in this case will be describedlater.

Next, the light flux projected from this beam-shaper 20 passes thecoupling lens 12 and the divergent light is converted into a parallellight, and via beam splitter 13, the light flux is projected in thecondition that the diameter of which is enlarged by the beam expander14, that is, the light flux diameter is enlarged more than that at thetime of incident. Then, the light flux passes the first objective lens16 a and is stopped down by the stop 15, and forms a light convergingspot on the information recording surface 31 through a protectivesubstrate 30 of the optical information recording medium by the secondobjective lens 16 b.

Then, the apparatus 10 is structured in such a manner that the lightflux modulated by an information pit on the information recordingsurface 31 and reflected passes again the first objective 16 a, stop 15,the second objective lens 16 b, beam expander 14, and is branched by thebeam splitter 13. Then, the astigmatism is given by the cylindrical lens17, and via the concave lens 18, the light flux is incident on the lightsensor 19, and by using a signal outputted from the light sensor 19, thereading signal of the information recorded in the optical informationrecording medium is obtained.

As shown in. FIG. 1, the beam-shaper 20 in the present embodiment is aplastic-made single lens which is a rotation asymmetrical lens.

The linear expansion coefficient α_(n) of the beam-shaper is in therange of 5.0×10⁻⁵<α_(n)<8.0×10⁻⁵.

The incident surface 21 of the beam-shaper 20 is formed as a rotationasymmetrical surface to the optical axis L.

FIG. 2 is a sectional view depressing the shape of a non-circular arctoroidal surface, and a dotted line in the view shows a light path ofthe light flux passing inside the beam-shaper 20. Hereupon, an equation(shape function) expressing the non-circular arc toroidal surface willbe described later.

The incident surface of the beam-shaper 20 is structured by a surface inwhich a non-circular line segment L1 (non-circular arc) in YZ surface isrotated around the axis (rotation axis A1) passing the central point ofa circular arc L2 of radius R=R1 in a plane orthogonal to thisnon-circular arc in Y direction.

The outgoing surface 22 of the beam-shaper 20 is formed of a toroidalsurface in which the radius of curvature in XZ surface is different fromthe radius of curvature in YZ surface.

Further, FIG. 5 is a view showing a fixing method of the beam-shaper 20to the optical pick-up, and as shown in FIG. 5( a), the outgoing surface22 side of the beam-shaper 20 is fixed to the optical pick-up apparatus10 main body by the fixing member, and is structured in such a mannerthat the position in the optical axis direction of the outgoing surface22 is not relatively and practically changed to the light source 11.Further, as shown in FIG. 5( b), the outgoing surface 22 side of thebeam-shaper 20 is directly to the optical pick-up apparatus 10 mainbody, and is structured in such a manner that the position in theoptical axis direction of the outgoing surface 22 is not relatively andpractically changed to the light source 11. Hereupon, in FIG. 5( a) andFIG. 5( b), the outgoing surface 22 side of the beam-shaper 20 is fixedto the optical pick-up apparatus 10 main body, however, the incidentsurface 21 side of the beam-shaper may also be fixed to the opticalpick-up apparatus 10 main body.

Then, the beam-shaper 20 converts the incident light flux whose crosssection is elliptical, to the light flux whose cross section is almostcircular, by the difference of the refractive power between XZ crosssection and YZ cross section, and projects the light flux.

Further, in the conventionally used beam-shaper 20, the astigmatism isgenerated at the time of change of the environmental temperature due toa reason that mainly the refractive power is different in XZ crosssection and YZ cross section. However, in the optical pick-up apparatusprovided with the beam-shaper 20 of the present invention, it isstructured in such a manner that the outgoing surface of the beam-shaper20 is fixed so that the position in the optical axis direction of theoutgoing surface of the beam-shaper 20 is not practically moved to thelight source, and because the distance change from the light source 11to the incident surface 21 activates in the direction to cancel theastigmatism, in turn, even when the astigmatism is generated, as theresult, the astigmatism is suppressed. Of course, because the shape isalso changed by the linear expansion of the beam-shaper 20 itself due tothe temperature change, the astigmatism can be further effectivelysuppressed.

When specifically described, it is structured in such a manner that, inthe cases where the refractive index of the beam-shaper 20 is changed bythe environmental temperature change and the change of the projectingangle (an angle formed between the advancing direction of the projectinglight flux and the optical axis L) of the light flux in XZ surface andYZ surface thereby, and the change of projecting angle due to a reasonthat, when the shape of the incident surface 21 and the outgoing surface22 is changed by the linear expansion, the refractive index of theincident surface 21 and the outgoing surface 22 is changed, and thechange of the projecting angle due to a reason that, when thebeam-shaper 20 is fixed so that the outgoing surface position is notchanged as described above, the position of the incident surface 21 isrelatively changed to the light source 11 by the linear expansion, arecombined, the direction of the focal line in XZ surface and YZ surfaceis adjusted, and also after the environmental temperature change, thegeneration of the astigmatism is suppressed.

Further, in the embodiment in this time, a fixing configuration so thatthe outgoing surface of the beam-shaper 20 is not practically changed inthe optical axis direction to the light source, is shown. However, aconfiguration fixing the incident surface side depending on thethickness of the beam-shaper or the specification of the optical pick-upapparatus may also be allowed, and in short, it may be allowed when itis a structure fixed so that the astigmatism generated due to thetemperature change is generated in the direction in which it iscancelled by the linear expansion of the beam-shaper 20.

Hereupon, as a member fixing the beam-shaper 20 to the apparatus, amaterial in which the linear expansion is not practically generated evenby the change of the environmental temperature, that is, a materialwhose linear expansion coefficient satisfies 1.0×10⁻⁵<αn<3.0×10⁻⁵, canbe used, for example, aluminum may also be used.

In the case of aluminum, the processability and the strength are higherthan those of resin, and it is appropriate as the member on the mainbody side to be fixed.

Hereupon, when the wavelength variation of the projected light flux isgenerated by the change of the environmental temperature, the designwork of the beam-shaper 20 is conducted, considering also the projectingangle change due to this wavelength variation.

As described above, according to the present invention, while thegeneration of the astigmatism following the change of the environmentaltemperature is suppressed, a plastic-made beam-shaper 20 by which thedivergent beam whose cross sectional shape is almost circular, can beprojected, and an optical pick-up apparatus 10 can be obtained.

Hereupon, the structure of the beam-shaper 20 and the optical pick-upapparatus 10 is not limited to those shown in the above embodiment. Forexample, in the above embodiment, the beam expander 14 and the objectivelens 16 are structured by a combination of respective 2 optical elements(the first beam expander 14 a and the second beam expander 14 b, thefirst objective lens 16 a and the second objective lens 16 b), however,it is not limited to this, they may also be respective lens compositionsof a single lens. Further, it may also be a structure of the opticalpick-up apparatus having so-called the compatibility by which therecording and/or reproducing of the information can be conducted on aplurality of kinds of optical information recording media by using aplurality of light fluxes whose wavelength are different.

Further, the diffractive structure may also be provided on the opticalsurface of the optical element constituting the optical pick-upapparatus 10. Hereby, the deterioration of the wave-front aberrationand/or astigmatism at the time of environmental temperature change usingthe diffraction light or at the time of the wavelength variation(mode-hop) of the light flux can be compensated for. Further, thewavelength selectivity by which the optical path difference is givenonly to the incident light flux of the specific wavelength, can be givento it, for example, even in the case where a plurality of kinds of lightfluxes whose wavelength are different are projected from the lightsource 11, the cross sectional shape can be shaped for each light flux.

FIG. 3 is a graph showing an example of a change of the remainedaberration (4thAs(tetraphyllous)) and the astigmatism (vertical axis) atthe time of the temperature change to the change of the designedthickness on the axis (quadrature axis) in the case where both of theincident surface and the outgoing surface of the beam-shaper 20 arestructured by cylindrical surfaces.

When both surfaces of the plastic-made beam-shaper are structured bycylindrical surfaces, the astigmatism to the temperature change can besuppressed to a degree of practically no hindrance, however, as shown inthe graph, it is not easy that the beam-shaper which can make theastigmatism at the time of the temperature change and the remainedaberration (4thAs(tetraphyllous aberration)) compatible with each other,is structured by both-surface cylindrical surface.

Accordingly, in order to make compatible the astigmatism at the time ofthe temperature change and the remained aberration (4thAs(tetraphyllousaberration)), it is preferable that at least one of the incident surfaceand the outgoing surface of the beam-shaper is structured by a toroidalsurface.

Hereupon, in the present embodiment, the beam-shaper 20 shapes theincident light flux, from the light source 11, whose cross sectionalshape is elliptical, into circular, however, it is not limited to this,the light flux may also be shaped to the elliptical shape in which thelong diameter and/or short diameter is different from that in the caseof the incidence.

Further, in the present embodiment, the beam-shaper 20 is arranged inthe vicinity of the light source 11, however, it is not limited to this,the beam-shaper 20 may be arranged in the optical path of the projectedlight flux.

Further, in the above embodiment, the light source 11 and thebeam-shaper 20 are separated structures, however, as shown in FIG. 6, itmay also be a structure in which the beam-shaper 20 is arranged in thevicinity of the light source 11, and they are housed in the same casing,hereby, a light source apparatus having a function by which, even at thetime of the environmental temperature change, the generation of theastigmatism is suppressed, is obtained.

Further, a case where the beam-shaper 20 is applied to the opticalpick-up apparatus 10, is described, however, it is not limited to this,the beam-shaper 20 can be applied for all of the apparatus such as, forexample, a laser beam printer or copier, in which the cross sectionalshape of the light flux is shaped to the circle and used.

EXAMPLES

Next, examples 1-6 will be described.

The optical pick-up apparatus in each example is the same structure asthat shown in FIG. 1.

As shown in Table 1, Examples 1-3 are examples in which the shapingmagnification m of the beam-shaper is constant, and S (a distance on theoptical axis from the light source to the incident surface of thebeam-shaper) and L (the thickness on the axis of the beam-shaper) ischanged, and Examples 4-6 are examples in which S is constant, and m andL are changed.

TABLE 1 Characteristics of Examples m fc S L L/S αn AS3(Δn) AS3(Δλ)AS3(ΔL) AS3(ΔS) AS3(total) (a) Ex. A1* 2.34 10 1 1.75 1.750 6.4 × E−50.019 0.001 −0.006 −0.013 0.001 Ex. A2* 2.34 10 1.5 2.6 1.733 6.4 × E−50.029 0.002 −0.011 −0.019 0.000 Ex. A3* 2.34 10 2 3.45 1.725 6.4 × E−50.038 0.002 −0.015 −0.025 0.000 (b) Ex. B1* 1.5 12 2 1.35 0.675 6.4 ×E−5 0.018 0.001 −0.012 −0.008 0.000 Ex. B2* 2 12 2 2.56 1.280 6.4 × E−50.034 0.002 −0.013 −0.020 0.002 Ex. B3* 2.5 12 2 3.11 1.555 6.4 × E−50.042 0.003 −0.018 −0.027 0.000 *Ex.: Example **αn: ×E−5 M: Bean shapingmagnification fc(mm): Focal distance of coupling lens S(mm): Distance onthe optical between the light source and the incident surface of thebeam-shaper L(mm): thickness on axis of the beam-shaper As3(Δn)(λrms):the astigmatism generated following the change of the refractive indexof the beam-shaper at the time of temperature change (+30° C.)(dn/dT =−1.2 × E−4 (1/° C.)) AS3(Δλ)(λrms): the astigmatism generated followingthe change of the oscillation wavelength of the light source at the timeof temperature change (+30° C.)(dn/dT = 5.0 × E−2 (nm/° C.))As3(ΔL)(λrms): the astigmatism generated by the shape change generatedwhen the beam-shaper is linear expanded at the time of temperaturechange (+30° C.) As3(ΔS)(λrms): the astigmatism generated by theinterval change between the light source and the beam-shaper incidentsurface generated when the beam-shaper is linear expanded at the time oftemperature change (+30° C.) As3(total)(λrms): the astigmatism generatedat the time of temperature change (+30° C.) (total of the above 4astigmatism)

The lens data of the optical element constituting each optical pick-upapparatus in Examples 1-6 is shown in Tables 2-7.

TABLE 2 Example 1 lens data   Light source wavelength λ = 405 nm   Distance from the light source to the beam-shaper       Z = 1.000 mm   Incident surface (beam-shaper)    Radius of curvature on XZ surface    R_(x) = −1.3672 × E−1 mm    Radius of curvature on YZ surface    R_(y) = −8.2203 × E−1 mm    Non-circular arc toroidal coefficient    κ_(y) = −0.0000 × E−0     A_(y4) = −4.6270 × E−1 Thickness on axis    D = 1.750 mm Refractive index   n(405 nm) = 1.525 Outgoing surface  Radius of curvature on XZ surface     R_(x) = −1.3228 × E−0 mm  Radius of curvature on YZ surface     R_(y) = −2.3097 × E−0 mmInterval (beam-shaper − coupling optical element)     Z = 5.911 mmIncident surface (coupling optical element)   Radius of curvature     R= +3.8964 × E+1 mm Thickness on axis     D = 2.000 mm Refractive index    n(405 nm) = 1.525 Outgoing surface   Radius of curvature     R =−5.9591 × E−0 mm   Aspheric surface coefficient     κ = −1.0000 × E−1    A₄ = +3.0567 × E−4     A₆ = +2.7065 × E−5 Interval (coupling opticalelement − beam-expander)     Z = 5.000 mm Incident surface (beamexpander)   Radius of curvature     R = −8.1743 × E+0 mm   Asphericsurface coefficient     κ = −2.9258 × E−1     A₄ = +6.4796 × E−3     A₆= +8.7198 × E−6 Thickness on axis     D = 0.800 mm Refractive index    n(405 nm) = 1.525 Outgoing surface   Radius of curvature     R =+2.3535 × E+1 mm   Aspheric surface coefficient     κ = −1.1221 × E+1    A₄ = −2.0771 × E−5     A₆ = +7.7561 × E−6 Interval (beam expanderinterval)     Z = 2.000 mm Incident surface (beam expander)   Radius ofcurvature     R = +1.0000 × E+20 mm   Optical path difference function(coefficient of   optical path difference function: reference  wavelength 405 nm)     C2 −2.4049 × E+1     C4 −2.2337 × E−1 Thicknesson axis     D = 1.000 mm Refractive index     n(405 nm) = 1.525 Outgoingsurface   Radius of curvature     R = −1.8017 × E+1 mm   Optical pathdifference function (coefficient of   optical path difference function:reference wavelength   405 nm)     C2 −2.6978 × E+1     C4 +2.2893 × E−2Interval (beam expander − stop)     Z = 10.00 mm Stop     φ3.000 mmInterval (stop − objective lens)     Z = 0.000 mm Incident surface(objective lens)   Radius of curvature     R = +2.0966 × E+0 mm  Aspheric surface coefficient     κ = −1.6811 × E−1     A₄ = −4.6833 ×E−3     A₆ = +6.1106 × E−4     A₈ = −9.4660 × E−4     A₁₀ = +2.3384 ×E−4     A₁₂ = −1.5568 × E−4     A₁₄ = +6.6382 × E−5     A₁₆ = −1.8857 ×E−5 Thickness on axis     D = 2.500 mm Refractive index     n(405 nm) =1.525 Outgoing surface   Radius of curvature     R = +6.2900 × E+0 mm  Aspheric surface coefficient     κ = −2.2155 × E−3     A₄ = +1.7541 ×E−2     A₆ = −9.5133 × E−3     A₈ = −1.7951 × E−2     A₁₀ = +8.9879 ×E−3 Interval (objective lens interval)     Z = 0.050 mm Incident surface(objective lens)   Radius of curvature     R = +8.8802 × E−1 mm  Aspheric surface coefficient     κ = −8.0927 × E−1     A₄ = +1.1694 ×E−1     A₆ = +2.8874 × E−2     A₈ = +1.2745 × E−1     A₁₀ = −8.7726 ×E−2 Thickness on axis     D = 1.100 mm Refractive index     n(405 nm) =1.560 Outgoing surface (objective lens)   Radius of curvature     R =+1.0000 × E+20 mm Interval (objective lens − disk)     Z = 0.256 mmSubstrate thickness     D = 0.100 mm Refractive index     n(405 nm) =1.619

TABLE 3 Example 2 lens data Light source wavelength     λ = 405 nmDistance from light source to beam-shaper     Z = 1.500 mm Incidentsurface (beam-shaper)   Radius of curvature on XZ surface     R_(x) =−2.0492 × E−1 mm   Radius of curvature on YZ surface     R_(y) = −1.2394× E−0 mm   non-circular arc toroidal coefficient     κ_(y) = −0.0000 ×E−0     A_(y4) = −1.3753 × E−1 Thickness on axis     D = 2.600 mmRefractive index     n(405 nm) = 1.525 Outgoing surface   Radius ofcurvature on XZ surface     R_(x) = −1.9680 × E−0 mm   Radius ofcurvature on YZ surface     R_(y) = −3.4591 × E−0 mm Interval(beam-shaper − coupling optical element)     Z = 4.483 mm Incidentsurface (coupling optical element)   Radius of curvature     R_(x) =+3.8964 × E+1 mm Thickness on axis     D = 2.000 mm Refractive index    n(405 nm) = 1.525 Outgoing surface   Radius of curvature     R =−5.9591 × E−0 mm   Aspheric surface coefficient     κ = −1.0000 × E−1    A₄ = +2.8099 × E−4     A₆ = +2.7162 × E−5 Interval (coupling opticalelement − beam expander)     Z = 5.000 mm Incident surface (beamexpander)   Radius of curvature     R = −8.1743 × E+0 mm   Asphericsurface coefficient     κ = −2.9258 × E−1     A₄ = +6.4796 × E−3     A₆= +8.7198 × E−6 Thickness on axis     D = 0.800 mm Refractive index    n(405 nm) = 1.525 Outgoing surface   Radius of curvature     R =+2.3535 × E+1 mm   Aspheric surface coefficient     κ = −1.1221 × E+1    A₄ = −2.0771 × E−5     A₆ = +7.7561 × E−6 Interval (beam expanderinterval)     Z = 2.000 mm Incident surface (beam expander)   Radius ofcurvature     R = +1.0000 × E+20 mm   Optical path difference function  (coefficient of optical path difference function:   referencewavelength 405 nm)     C2 −2.4049 × E+1     C4 −2.2337 × E−1 Thicknesson axis     D = 1.000 mm Refractive index     n(405 nm) = 1.525 Outgoingsurface   Radius of curvature     R = −1.8017 × E+1 mm   Optical pathdifference function   (coefficient of optical path difference function:  reference wavelength 405 nm)     C2 −2.6978 × E+1     C4 +2.2893 × E−2Interval (beam expander − stop)     Z = 10.00 mm Stop     φ 3.000 mmInterval (stop − objective lens)     Z = 0.000 mm Incident surface(objective lens)   Radius of curvature     R = +2.0966 × E+0 mm  Aspheric surface coefficient     κ = −1.6811 × E−1     A₄ = −4.6833 ×E−3     A₆ = +6.1106 × E−4     A₈ = −9.4660 × E−4     A₁₀ = +2.3384 ×E−4     A₁₂ = −1.5568 × E−4     A₁₄ = +6.6382 × E−5     A₁₆ = −1.8857 ×E−5 Thickness on axis     D = 2.500 mm Refractive index     n(405 nm) =1.525 Outgoing surface   Radius of curvature     R = +6.2900 × E+0 mm  Aspheric surface coefficient     κ = −2.2155 × E−3     A₄ = +1.7541 ×E−2     A₆ = −9.5133 × E−3     A₈ = −1.7951 × E−2     A₁₀ = +8.9879 ×E−3 Interval (objective lens interval)     Z = 0.050 mm Incident surface(objective lens)   Radius of curvature     R = +8.8802 × E−1 mm  Aspheric surface coefficient     κ = −8.0927 × E−1     A₄ = +1.1694 ×E−1     A₆ = +2.8874 × E−2     A₈ = +1.2745 × E−1     A₁₀ = −8.7726 ×E−2 Thickness on axis     D = 1.100 mm Refractive index     n(405 nm) =1.560 Outgoing surface (objective lens)   Radius of curvature     R =+1.0000 × E+20 mm Interval (objective lens − disk)     Z = 0.256 mmSubstrate thickness     D = 0.100 mm Refractive index     n(405 nm) =1.619

TABLE 4 Example 3 lens data Light source wavelength     λ = 405 nmDistance from light source to beam-shaper     Z = 2.000 mm Incidentsurface (beam-shaper)   Radius of curvature on XZ surface     R_(x) =−2.7314 × E−1 mm   Radius of curvature on YZ surface     R_(y) = −1.6572× E−0 mm   Non-circular arc toroidal coefficient     κ_(y) = −0.0000 ×E−0     A_(y4) = −5.8133 × E−2 Thickness on axis     D = 3.450 mmRefractive index     n(405 nm) = 1.525 Outgoing surface   Radius ofcurvature on XZ surface     R_(x) = −2.6142 × E−0 mm   Radius ofcurvature on YZ surface     R_(y) = −4.6120 × E−0 mm Interval(beam-shaper − coupling optical element)     Z = 3.058 mm Incidentsurface (coupling optical element)   Radius of curvature     R = +3.8964× E+1 mm Thickness on axis     D = 2.000 mm Refractive index     n(405nm) = 1.525 Outgoing surface   Radius of curvature     R = −5.9591 × E−0mm   Aspheric surface coefficient     κ = −1.0000 × E−1     A₄ = +2.5641× E−4     A₆ = +2.7218 × E−5 Interval (coupling optical element − beamexpander)     Z = 5.000 mm Incident surface (beam expander)   Radius ofcurvature     R = −8.1743 × E+0 mm   Aspheric surface coefficient     κ= −2.9258 × E−1     A₄ = +6.4796 × E−3     A₆ = +8.7198 × E−6 Thicknesson axis     D = 0.800 mm Refractive index     n(405 nm) = 1.525 Outgoingsurface   Radius of curvature     R = +2.3535 × E+1 mm   Asphericsurface coefficient     κ = −1.1221 × E+1     A₄ = −2.0771 × E−5     A₆= +7.7561 × E−6 Interval (beam expander interval)     Z = 2.000 mmIncident surface (beam expander)   Radius of curvature     R = +1.0000 ×E+20 mm   Optical path difference function   (coefficient of opticalpath difference function:   reference wavelength 405 nm)     C2 −2.4049× E+1     C4 −2.2337 × E−1 Thickness on axis     D = 1.000 mm Refractiveindex     n(405 nm) = 1.525 Outgoing surface   Radius of curvature     R= −1.8017 × E+1 mm   Optical path difference function   (coefficient ofoptical path difference function:   reference wavelength 405 nm)     C2−2.6978 × E+1     C4 +2.2893 × E−2 Interval (beam expander − stop)     Z= 10.00 mm Stop     φ 3.000 mm Interval (stop − objective lens)     Z =0.000 mm Incident surface (objective lens)   Radius of curvature     R =+2.0966 × E+0 mm   Aspheric surface coefficient     κ = −1.6811 × E−1    A₄ = −4.6833 × E−3     A₆ = +6.1106 × E−4     A₈ = −9.4660 × E−4    A₁₀ = +2.3384 × E−4     A₁₂ = −1.5568 × E−4     A₁₄ = +6.6382 × E−5    A₁₆ = −1.8857 × E−5 Thickness on axis     D = 2.500 mm Refractiveindex     n(405 nm) = 1.525 Outgoing surface   Radius of curvature     R= +6.2900 × E+0 mm   Aspheric surface coefficient     κ = −2.2155 × E−3    A₄ = +1.7541 × E−2     A₆ = −9.5133 × E−3     A₈ = −1.7951 × E−2    A₁₀ = +8.9879 × E−3 Interval (objective lens interval)     Z = 0.050mm Incident surface (objective lens)   Radius of curvature     R =+8.8802 × E−1 mm   Aspheric surface coefficient     κ = −8.0927 × E−1    A₄ = +1.1694 × E−1     A₆ = +2.8874 × E−2     A₈ = +1.2745 × E−1    A₁₀ = −8.7726 × E−2 Thickness on axis     D = 1.100 mm Refractiveindex     n(405 nm) = 1.560 Outgoing surface (objective lens)   Radiusof curvature     R = +1.0000 × E+20 mm Interval (objective lens − disk)    Z = 0.256 mm Substrate thickness     D = 0.100 mm Refractive index    n(405 nm) = 1.619

TABLE 5 Example 4 lens data Light source wavelength     λ = 405 nmDistance from light source to beam-shaper     Z = 2.000 mm Incidentsurface (beam-shaper)   Radius of curvature on XZ surface     R_(x) =−4.6475 × E−1 mm   Radius of curvature on YZ surface     R_(y) = −2.3060× E−0 mm   Non-circular arc toroidal coefficient     κ_(y) = −0.0000 ×E−0     A_(y4) = +7.5152 × E−3 Thickness on axis     D = 1.350 mmRefractive index     n(405 nm) = 1.525 Outgoing surface   Radius ofcurvature on XZ surface     R_(x) = −1.2127 × E−0 mm   Radius ofcurvature on YZ surface     R_(y) = −2.5200 × E−0 mm Interval(beam-shaper − coupling optical element)     Z = 6.560 mm Incidentsurface (coupling optical element)   Radius of curvature     R = +5.0247× E+1 mm Thickness on axis     D = 2.000 mm Refractive index     n(405nm) = 1.525 Outgoing surface   Radius of curvature     R = −7.1036 × E−0mm   Aspheric surface coefficient     κ = −1.0000 × E−1     A₄ = +2.0406× E−4     A₆ = +2.2179 × E−5 Interval (coupling optical element − beamexpander)     Z = 5.000 mm Incident surface (beam expander)   Radius ofcurvature     R = −8.1743 × E+0 mm   Aspheric surface coefficient     κ= −2.9258 × E−1     A₄ = +6.4796 × E−3     A₆ = +8.7198 × E−6 Thicknesson axis     D = 0.800 mm Refractive index     n(405 nm) = 1.525 Outgoingsurface   Radius of curvature     R = +2.3535 × E+1 mm   Asphericsurface coefficient     κ = −1.1221 × E+1     A₄ = −2.0771 × E−5     A₆= +7.7561 × E−6 Interval (beam expander interval)     Z = 2.000 mmIncident surface (beam expander)   Radius of curvature     R = +1.0000 ×E+20 mm   Optical path difference function (coefficient of optical pathdifference function: reference wavelength 405 nm)     C2 −2.4049 × E+1    C4 −2.2337 × E−1 Thickness on axis     D = 1.000 mm Refractive index    n(405 nm) = 1.525 Outgoing surface   Radius of curvature     R =−1.8017 × E+1 mm   Optical path difference function (coefficient ofoptical path difference function: reference wavelength 405 nm)     C2−2.6978 × E+1     C4 +2.2893 × E−2 Interval (beam expander − stop)     Z= 10.00 mm Stop     φ 3.000 mm Interval (stop − objective lens)     Z =0.000 mm Incident surface (objective lens)   Radius of curvature     R =+2.0966 × E+0 mm   Aspheric surface coefficient     κ = −1.6811 × E−1    A₄ = −4.6833 × E−3     A₆ = +6.1106 × E−4     A₈ = −9.4660 × E−4    A₁₀ = +2.3384 × E−4     A₁₂ = −1.5568 × E−4     A₁₄ = +6.6382 × E−5    A₁₆ = −1.8857 × E−5 Thickness on axis     D = 2.500 mm Refractiveindex     n(405 nm) = 1.525 Outgoing surface (objective lens)   Radiusof curvature     R = +6.2900 × E+0 mm   Aspheric surface coefficient    κ = −2.2155 × E−3     A₄ = +1.7541 × E−2     A₆ = −9.5133 × E−3    A₈ = −1.7951 × E−2     A₁₀ = +8.9879 × E−3 Interval (objective lensinterval)     Z = 0.050 mm Incident surface (objective lens)   Radius ofcurvature     R = +8.8802 × E−1 mm   Aspheric surface coefficient     κ= −8.0927 × E−1     A₄ = +1.1694 × E−1     A₆ = +2.8874 × E−2     A₈ =+1.2745 × E−1     A₁₀ = −8.7726 × E−2 Thickness on axis     D = 1.100 mmRefractive index     n(405 nm) = 1.560 Outgoing surface (objective lens)  Radius of curvature     R = +1.0000 × E+20 mm Interval (objective lens− disk)     Z = 0.256 mm Substrate thickness     D = 0.100 mm Refractiveindex     n(405 nm) = 1.619

TABLE 6 Example 5 lens data Light source wavelength     λ = 405 nmDistance from light source to beam-shaper     Z = 2.000 mm Incidentsurface (beam-shaper)   Radius of curvature on XZ surface     R_(x) =−3.3226 × E−1 mm   Radius of curvature on YZ surface     R_(y) = −1.9469× E−0 mm   Non-circular arc toroidal coefficient     κ_(y) = −0.0000 ×E−0     A_(y4) = −4.1077 × E−3 Thickness on axis     D = 2.560 mmRefractive index     n(405 nm) = 1.525 Outgoing surface   Radius ofcurvature on XZ surface     R_(x) = −1.7774 × E−0 mm   Radius ofcurvature on YZ surface     R_(y)= −3.1233 × E−0 mm Interval(beam-shaper − coupling optical element)     Z = 4.867 mm Incidentsurface (coupling optical element)   Radius of curvature     R = +5.0247× E+1 mm Thickness on axis     D = 2.000 mm Refractive index     n(405nm) = 1.525 Outgoing surface   Radius of curvature     R = −7.1036 × E−0mm   Aspheric surface coefficient     κ = −1.0000 × E−1     A₄ = +1.7507× E−4     A₆ = +2.1905 × E−5 Interval (coupling optical element − beamexpander)     Z = 5.000 mm Incident surface (beam expander)   Radius ofcurvature     R = −8.1743 × E+0 mm   Aspheric surface coefficient     κ= −2.9258 × E−1     A₄ = +6.4796 × E−3     A₆ = +8.7198 × E−6 Thicknesson axis     D = 0.800 mm Refractive index     n(405 nm) = 1.525 Outgoingsurface   Radius of curvature     R = +2.3535 × E+1 mm   Asphericsurface coefficient     κ = −1.1221 × E+1     A₄ = −2.0771 × E−5     A₆= +7.7561 × E−6 Interval (beam expander interval)     Z = 2.000 mmIncident surface (beam expander)   Radius of curvature     R = +1.0000 ×E+20 mm   Optical path difference function   (coefficient of opticalpath difference function:   reference wavelength 405 nm)     C2 −2.4049× E+1     C4 −2.2337 × E−1 Thickness on axis     D = 1.000 mm Refractiveindex     n(405 nm) = 1.525 Outgoing surface   Radius of curvature     R= −1.8017 × E+1 mm   Optical path difference function   (coefficient ofoptical path difference function:   reference wavelength 405 nm)     C2−2.6978 × E+1     C4 +2.2893 × E−2 Interval (beam expander − stop)     Z= 10.00 mm Stop     φ 3.000 mm Interval (stop − objective lens)     Z =0.000 mm Incident surface (objective lens)   Radius of curvature     R =+2.0966 × E+0 mm   Aspheric surface coefficient     κ = −1.6811 × E−1    A₄ = −4.6833 × E−3     A₆ = +6.1106 × E−4     A₈ = −9.4660 × E−4    A₁₀ = +2.3384 × E−4     A₁₂ = −1.5568 × E−4     A₁₄ = +6.6382 × E−5    A₁₆ = −1.8857 × E−5 Thickness on axis     D = 2.500 mm Refractiveindex     n(405 nm) = 1.525 Outgoing surface (objective lens)   Radiusof curvature     R = +6.2900 × E+0 mm   Aspheric surface coefficient    κ = −2.2155 × E−3     A₄ = +1.7541 × E−2     A₆ = −9.5133 × E−3    A₈ = −1.7951 × E−2     A₁₀ = +8.9879 × E−3 Interval (objective lensinterval)     Z = 0.050 mm Incident surface (objective lens)   Radius ofcurvature     R = +8.8802 × E−1 mm   Aspheric surface coefficient     κ= −8.0927 × E−1     A₄ = +1.1694 × E−1     A₆ = +2.8874 × E−2     A₈ =+1.2745 × E−1     A₁₀ = −8.7726 × E−2 Thickness on axis     D = 1.100 mmRefractive index     n(405 nm) = 1.560 Outgoing surface (objective lens)  Radius of curvature     R = +1.0000 × E+20 mm Interval (objective lens− disk)     Z = 0.256 mm Substrate thickness     D = 0.100 mm Refractiveindex     n(405 nm) = 1.619

TABLE 7 Example 6 lens data Light source wavelength     λ = 405 nmDistance from light source to beam-shaper     Z = 2.000 mm Incidentsurface (beam-shaper)   Radius of curvature on XZ surface     R_(x) =−2.5901 × E−1 mm   Radius of curvature on YZ surface     R_(y) = −2.1024× E−0 mm   Non-circular arc toroidal coefficient     κ_(y) = −0.0000 ×E−0     A_(y4) = −1.2959 × E−3 Thickness on axis     D = 3.110 mmRefractive index     n(405 nm) = 1.525 Outgoing surface   Radius ofcurvature on XZ surface     R_(x) = −2.0275 × E−0 mm   Radius ofcurvature on YZ surface     R_(y) = −3.6277 × E−0 mm Interval(beam-shaper − coupling optical element)     Z = 4.239 mm Incidentsurface (coupling optical element)   Radius of curvature     R = +5.0247× E+1 mm Thickness on axis     D = 2.000 mm Refractive index     n(405nm) = 1.525 Outgoing surface   Radius of curvature     R = −7.1036 × E−0mm   Aspheric surface coefficient     κ = −1.0000 × E−1     A₄ = +1.5525× E−4     A₆ = +2.1947 × E−5 Interval (coupling optical element − beamexpander)     Z = 5.000 mm Incident surface (beam expander)   Radius ofcurvature     R = −8.1743 × E+0 mm   Aspheric surface coefficient     κ= −2.9258 × E−1     A₄ = +6.4796 × E−3     A₆ = +8.7198 × E−6 Thicknesson axis     D = 0.800 mm Refractive index     n(405 nm) = 1.525 Outgoingsurface   Radius of curvature     R = +2.3535 × E+1 mm   Asphericsurface coefficient     κ = −1.1221 × E+1     A₄ = −2.0771 × E−5     A₆= +7.7561 × E−6 Interval (beam expander interval)     Z = 2.000 mmIncident surface (beam expander)   Radius of curvature     R = +1.0000 ×E+20 mm   Optical path difference function (coefficient of optical pathdifference function: reference wavelength 405 nm)     C2 −2.4049 × E+1    C4 −2.2337 × E+1 Thickness on axis     D = 1.000 mm Refractive index    n(405 nm) = 1.525 Outgoing surface   Radius of curvature     R =−1.8017 × E+1 mm   Optical path difference function (coefficient ofoptical path difference function: reference wavelength 405 nm)     C2−2.6978 × E+1     C4 +2.2893 × E−2 Interval (beam expander − stop)     Z= 10.00 mm Stop     φ 3.000 mm Interval (stop − objective lens)     Z =0.000 mm Incident surface (objective lens)   Radius of curvature     R =+2.0966 × E+0 mm   Aspheric surface coefficient     κ = −1.6811 × E−1    A₄ = −4.6833 × E−3     A₆ = +6.1106 × E−4     A₈ = −9.4660 × E−4    A₁₀ = +2.3384 × E−4     A₁₂ = −1.5568 × E−4     A₁₄ = +6.6382 × E−5    A₁₆ = −1.8857 × E−5 Thickness on axis     D = 2.500 mm Refractiveindex     n(405 nm) = 1.525 Outgoing surface (objective lens)   Radiusof curvature     R = +6.2900 × E+0 mm   Aspheric surface coefficient    κ = −2.2155 × E−3     A₄ = +1.7541 × E−2     A₆ = −9.5133 × E−3    A₈ = −1.7951 × E−2     A₁₀ = +8.9879 × E−3 Interval (objective lensinterval)     Z = 0.050 mm Incident surface (objective lens)   Radius ofcurvature     R = +8.8802 × E−1 mm   Aspheric surface coefficient     κ= −8.0927 × E−1     A₄ = +1.1694 × E−1     A₆ = +2.8874 × E−2     A₈ =+1.2745 × E−1     A₁₀ = −8.7726 × E−2 Thickness on axis     D = 1.100 mmRefractive index     n(405 nm) = 1.560 Outgoing surface (objective lens)  Radius of curvature     R = +1.0000 × E+20 mm Interval (objective lens− disk)     Z = 0.256 mm Substrate thickness     D = 0.100 mm Refractiveindex     n(405 nm) = 1.619

The incident surface of the beam-shaper is structured by thenon-circular arc toroidal surface which is regulated by the equation inwhich coefficients shown in Tables 2-7 are substituted into Math-1.

$\begin{matrix}{{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{R_{y}\left( {1 + \sqrt{\left. {1 - {\left( {1 + k_{y}} \right){Y^{2}/R_{y}^{2}}}} \right)}} \right.} + {\sum\limits_{i}{A_{yi}Y^{i}}}} \right)^{2}} & \left\lbrack {{Math}\text{-}1} \right\rbrack\end{matrix}$

Herein, Z is a distance in the optical axis L direction (an advancingdirection of the light is positive), X, Y are distances in X-directiondirection, Y-direction (height from the optical axis), R_(x) is aparaxial radius of curvature on XZ surface, R_(y) is a paraxial radiusof curvature on YZ surface, k_(y) and A_(yi) are non-circular arccoefficients.

Hereupon, in Tables 2-7, for example, “−1.3672×E−1” means“−1.3672×10⁻¹”.

The outgoing surface of the beam-shaper is structured by a toroidalsurface regulated by an equation in which coefficients shown in Tables2-7 are substituted into Math-3.

$\begin{matrix}{{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{\left( {1 + \sqrt{\left. {1 - {Y^{2}/R_{y}^{2}}} \right)}} \right.}} \right)} & \left\lbrack {{Math}\text{-}3} \right\rbrack\end{matrix}$

Further, the incident surface of the coupling lens (coupring opticalelement) and the outgoing surface of the second objective lens arerespectively formed into a spherical surface of the radius of curvatureR around the optical axis.

Further, the outgoing surface of the coupling lens, incident surface andoutgoing surface of the first beam expander, incident surface andoutgoing surface of the first objective lens, and incident surface ofthe second objective lens are respectively formed into the asphericsurface which is axially symmetric around the optical axis L, regulatedby the equation in which coefficients shown in Tables 2-7 aresubstituted into Math-5.

$\begin{matrix}{{{Aspheric}\mspace{14mu}{surface}\mspace{14mu}{shape}\mspace{14mu}{equation}}{z = {\frac{\left( {h^{2}/r_{i}} \right)}{1 + \sqrt{1 - {\left( {1 + \kappa} \right)\left( {h/r_{i}} \right)^{2}}}} + {\sum\limits_{i = 0}{A_{2i}h^{2i}}}}}} & \left\lbrack {{Math}\text{-}5} \right\rbrack\end{matrix}$

Herein, κ is a conical coefficient, A_(2i) is an aspheric surfacecoefficient, h is a distance from the optical axis. Further, thediffraction ring-shaped zone around the optical axis is formed on theincident surface and the outgoing surface of the second beam expander,and a pitch of the diffraction ring-shaped zone is regulated by theequation in which coefficients shown in Tables 2-7 are substituted intothe optical path difference function of Math-6.

$\begin{matrix}{{{Optical}\mspace{14mu}{path}\mspace{14mu}{difference}\mspace{14mu}{function}}\text{}{{\phi\;(h)} = {\sum\limits_{i = 0}{C_{2i}h^{2i}}}}} & \left\lbrack {{Math}\text{-}6} \right\rbrack\end{matrix}$

Herein, C2i is a coefficient of the optical path difference function.

Hereupon, in Tables 2-7, “reference wavelength” indicates so-called theblaze wavelength, and a wavelength in which, when the light flux havingthat wavelength is incident on the lens, the diffraction efficiency ofthe diffraction light of all-orders generated by the diffractivestructure is the maximum (for example, 100%).

AS3 (total) of Table 1(a) and (b) shows, when the temperature rises 30°C., a total of 4 astigmatisms (AS3(Δn), AS3(Δλ), AS3(ΔL), AS3(ΔS)).

According to the beam-shaper and the optical pick-up apparatus in thepresent embodiment, it can be seen from Table 1 that, even when theenvironmental temperature is changed, the generation of the astigmatismcan be suppressed.

In the structure of Examples 1-3, Table 8(a) is a graph expressing therelationship between a change amount of the astigmatism AS3 at the timeof the environmental temperature change and L when S is changed such asS=1, 1.5, 2.0.

In the structure of Examples 4-6, Table 8(b) is a graph expressing therelationship between L/S and the shaping magnification m.

From Table 8(a), it can be seen that a change amount of the astigmatismat the time of temperature change can be suppressed to almost zero, whenthe optical pick-up apparatus and the beam-shaper are designed by havingan eye to a fact that the proportional relationship is attained betweenS and L.

From Table 8(b), when the relationship between L/S and m is perceived,in the optical pick-up apparatus and the beam-shaper, a generationamount of the astigmatism at the time of temperature change can besuppressed. Specifically, when the beam shaping magnification isincreased, the refractive power in X direction and in Y direction islargely different, and a change amount of the astigmatism at the time oftemperature change is increased. Therefore, when L/S is increased, thechange amount of the astigmatism at the time of temperature change canbe suppressed.

Next, Examples 7-11 will be described.

The optical pick-up apparatus in each Example is the same structure asthat shown in FIG. 4, and a detailed description is neglected, however,a beam expander 14 is removed from the structure of the optical pick-upapparatus 10 shown in FIG. 1, and the objective lens 16 is structured bya single lens.

In the beam-shaper of Example 7, both of the incident surface (the thirdsurface) and the outgoing surface (the fourth surface) are structured bya cylindrical surface, and the surface shape of the incident surface isregulated by the equation in which coefficients shown in Table 9 aresubstituted into Math-1.

Hereupon, as in Example 7, when the cylindrical surface is regulated byusing Math-1, Math-3, R_(x)=∞ is substituted into Math-1, Math-3, andwhen the cylindrical surface is regulated by using Math-2, Math-4,R_(y)=∞ is substituted into Math-2, Math-4.

In the beam-shaper of Example 8, the incident surface is structured by atoroidal surface shown in Math-4, and the outgoing surface is structuredby a non-circular arc toroidal surface shown in Math-1, and the surfaceshape of the incident surface and outgoing surface is regulated by anequation in which coefficients shown in Table 10 are substituted intoeach expression.

In the beam-shaper of Example 9, the incident surface is structured by atoroidal surface shown in Math-4, and the outgoing surface is structuredby a non-circular arc toroidal surface shown in Math-1, and the surfaceshape of the incident surface and outgoing surface is regulated by anequation in which coefficients shown in Table 11 are substituted intoeach expression.

In the beam-shaper of Example 10, the incident surface is structured bya toroidal surface shown in Math-3, and the outgoing surface isstructured by a non-circular arc toroidal surface shown in Math-2, andthe surface shape of the incident surface and outgoing surface isregulated by an equation in which coefficients shown in Table 12 aresubstituted into each expression.

In the beam-shaper of Example 11, the incident surface is structured bya toroidal surface shown in Math-3, and the outgoing surface isstructured by a non-circular arc toroidal surface shown in Math-1, andthe surface shape of the incident surface and outgoing surface isregulated by an equation in which coefficients shown in Table 13 aresubstituted into each expression.

TABLE 9 Example 7 lens data 407 nm X Y object point side NA 0.145 0.057image point side NA 0.650 0.650 wave-front aberration 0.010 λtetraphyllious aberration 0.009 λ temperature characteristic −0.001 λ *1*1: astigmatism generated at ΔT = +30° C. i-th surface r_(yi) r_(xi)d_(i)(407 nm) n_(i)(407 nm) 0 0.2513 1 ∞ ∞ 0.2500 1.52994 2 ∞ ∞ 1.18530.00000 3 −0.2520 ∞ 2.0000 1.52461 4 −2.0871 ∞ 2.0000 1.00000 5 ∞ ∞8.0000 1.52994 6 ∞ ∞ 2.2810 1.00000 7 32.4251 32.4251 2.0000 1.52461 8−8.8439 −8.8439 5.0000 1.00000 9 ∞ ∞ 0.0000 1.00000 10 1.9327 1.93271.8500 1.55981 11 −11.3206 −11.3206 1.5567 1.00000 12 ∞ ∞ 0.6000 1.6186913 ∞ ∞ 0.0000 1.00000 The 3rd surface cylindrical surface The 4thsurface cylindrical surface A_(y4) = −9.5723E−04 The 8th surfaceaspheric surface coefficient κ = −1.0000E−01 A₄ = 1.4465E−04 A₆ =1.5346E−06 The 10th surface aspheric surface coefficient κ = −5.4726E−01A₄ = 3.7831E−04 A₆ = −1.8413E−03 A₈ = 6.4043E−04 A₁₀ = −9.8987E−05 A₁₂ =−1.1518E−06 A₁₄ = −7.9320E−07 Optical path difference function(Coefficient of optical path difference function: reference wavelength422 nm, diffraction order 8th-order (407 nm)) C₂ = −7.7249E−04 C₄ =−2.0466E−04 C₆ = −8.5677E−05 C₈ = 2.6999E−05 C₁₀ = −4.1167E−06 The 11thsurface aspheric surface coefficient κ = −3.3066E+02 A4 = −3.7387E−03 A6= 8.8025E−03 A8 = −5.2282E−03 A10 = 1.4815E−03 A12 = −2.1825E−04 A14 =1.3236E−05

TABLE 10 Example 8 lens data 407 nm X Y object point side NA 0.145 0.057image point side NA 0.650 0.650 wave-front aberration 0.008 λtetraphyllious aberration 0.007 λ temperature characteristic 0.000 λ *1*1: astigmatism generated at ΔT = +30° C. i-th surface r_(yi) r_(xi)d_(i)(407 nm) n_(i)(407 nm) 0 0.2513 1 ∞ ∞ 0.2500 1.52994 2 ∞ ∞ 1.18530.00000 3 −0.2530 −243.2876 2.0000 1.52461 4 −2.0865 −798.7465 2.00001.00000 5 ∞ ∞ 8.0000 1.52994 6 ∞ ∞ 2.2810 1.00000 7 32.4251 32.42512.0000 1.52461 8 −8.8439 −8.8439 5.0000 1.00000 9 ∞ ∞ 0.0000 1.00000 101.9327 1.9327 1.8500 1.55981 11 −11.3206 −11.3206 1.5567 1.00000 12 ∞ ∞0.6000 1.61869 13 ∞ ∞ 0.0000 1.00000 The 3rd surface X toroidal surfaceThe 4th surface X toroidal surface coefficient κ_(x) = −1.9988E+01A_(y4) = −1.9289E−03 The 8th surface aspheric surface coefficient κ =−1.0000E−01 A₄ = 1.5011E−04 A₆ = 1.0869E−06 The 10th surface asphericsurface coefficient κ = −5.4726E−01 A₄ = 3.7831E−04 A₆ = −1.8413E−03 A₈= 6.4043E−04 A₁₀ = −9.8987E−05 A₁₂ = −1.1518E−06 A₁₄ = −7.9320E−07Optical path difference function (Coefficient of optical path differencefunction: reference wavelength 422 nm, diffraction order 8th-order (407nm)) C₂ = −7.7249E−04 C₄ = −2.0466E−04 C₆ = −8.5677E−05 C₈ = 2.6999E−05C₁₀ = −4.1167E−06 The 11th surface aspheric surface coefficient κ =−3.3066E+02 A4 = −3.7387E−03 A6 = 8.8025E−03 A8 = −5.2282E−03 A10 =1.4815E−03 A12 = −2.1825E−04 A14 = 1.3236E−05

TABLE 11 Example 9 lens data 407 nm X Y object point side NA 0.145 0.057image point side NA 0.650 0.650 wave-front aberration 0.007 λtetraphyllious aberration 0.005 λ temperature characteristic 0.002 λ *1*1: astigmatism generated at ΔT = +30° C. i-th surface r_(yi) r_(xi)d_(i)(407 nm) n_(i)(407 nm) 0 0.2513 1 ∞ ∞ 0.2500 1.52994 2 ∞ ∞ 1.18530.00000 3 −0.2522 −520.6418 2.0000 1.52461 4 −2.0865 −742.0544 2.00001.00000 5 ∞ ∞ 8.0000 1.52994 6 ∞ ∞ 2.2810 1.00000 7 32.4251 32.42512.0000 1.52461 8 −8.8439 −8.8439 5.0000 1.00000 9 ∞ ∞ 0.0000 1.00000 101.9327 1.9327 1.8500 1.55981 11 −11.3206 −11.3206 1.5567 1.00000 12 ∞ ∞0.6000 1.61869 13 ∞ ∞ 0.0000 1.00000 The 3rd surface X toroidal surfaceThe 4th surface Y toroidal surface coefficient κ_(y) = −2.6114E+00A_(y4) = −3.8307E−02 The 8th surface aspheric surface coefficient κ =−1.0000E−01 A₄ = 1.5303E−04 A₆ = 5.6664E−07 The 10th surface asphericsurface coefficient κ = −5.4726E−01 A₄ = 3.7831E−04 A₆ = −1.8413E−03 A₈= 6.4043E−04 A₁₀ = −9.8987E−05 A₁₂ = −1.1518E−06 A₁₄ = −7.9320E−07Optical path difference function (Coefficient of optical path differencefunction: reference wavelength 422 nm, diffraction order 8th-order (407nm)) C₂ = −7.7249E−04 C₄ = −2.0466E−04 C₆ = −8.5677E−05 C₈ = 2.6999E−05C₁₀ = −4.1167E−06 The 11th surface aspheric surface coefficient κ =−3.3066E+02 A₄ = −3.7387E−03 A₆ = 8.8025E−03 A₈ = −5.2282E−03 A₁₀ =1.4815E−03 A₁₂ = −2.1825E−04 A₁₄ = 1.3236E−05

TABLE 12 Example 10 lens data 407 nm X Y object point side NA 0.1450.057 image point side NA 0.650 0.650 wave-front aberration 0.009 λtetraphyllious aberration 0.007 λ temperature characteristic −0.001 λ *1*1: astigmatism generated at ΔT = +30° C. i-th surface r_(yi) r_(xi)d_(i)(407 nm) n_(i)(407 nm) 0 0.2513 1 ∞ ∞ 0.2500 1.52994 2 ∞ ∞ 1.18530.00000 3 −0.2530 −280.0335 2.0000 1.52461 4 −2.0872 −1013.4197 2.00001.00000 5 ∞ ∞ 8.0000 1.52994 6 ∞ ∞ 2.2810 1.00000 7 32.4251 32.42512.0000 1.52461 8 −8.8439 −8.8439 5.0000 1.00000 9 ∞ ∞ 0.0000 1.00000 101.9327 1.9327 1.8500 1.55981 11 −11.3206 −11.3206 1.5567 1.00000 12 ∞ ∞0.6000 1.61869 13 ∞ ∞ 0.0000 1.00000 The 3rd surface Y toroidal surfaceThe 4th surface X toroidal surface coefficient κ_(x) = −1.9967E+01A_(x4) = −1.8665E−03 The 8th surface aspheric surface coefficient κ =−1.0000E−01 A₄ = 1.4882E−04 A₆ = 1.2613E−06 The 10th surface asphericsurface coefficient κ = −5.4726E−01 A₄ = 3.7831E−04 A₆ = −1.8413E−03 A₈= 6.4043E−04 A₁₀ = −9.8987E−05 A₁₂ = −1.1518E−06 A₁₄ = −7.9320E−07Optical path difference function (Coefficient of optical path differencefunction: reference wavelength 422 nm, diffraction order 8th-order (407nm)) C₂ = −7.7249E−04 C₄ = −2.0466E−04 C₆ = −8.5677E−05 C₈ = 2.6999E−05C₁₀ = −4.1167E−06 The 11th surface aspheric surface coefficient κ =−3.3066E+02 A₄ = −3.7387E−03 A₆ = 8.8025E−03 A₈ = −5.2282E−03 A₁₀ =1.4815E−03 A₁₂ = −2.1825E−04 A₁₄ = 1.3236E−05

TABLE 13 Example 11 lens data 407 nm X Y object point side NA 0.1450.057 image point side NA 0.650 0.650 wave-front aberration 0.006 λtetraphyllious aberration 0.005 λ temperature characteristic −0.001 λ *1*1: astigmatism generated at ΔT = +30° C. i-th surface r_(yi) r_(xi)d_(i)(407 nm) n_(i)(407 nm) 0 0.2513 1 ∞ ∞ 0.2500 1.52994 2 ∞ ∞ 1.18530.00000 3 −0.2522 −430.0049 2.0000 1.52461 4 −2.0866 −620.3211 2.00001.00000 5 ∞ ∞ 8.0000 1.52994 6 ∞ ∞ 2.2810 1.00000 7 32.4251 32.42512.0000 1.52461 8 −8.8439 −8.8439 5.0000 1.00000 9 ∞ ∞ 0.0000 1.00000 101.9327 1.9327 1.8500 1.55981 11 −11.3206 −11.3206 1.5567 1.00000 12 ∞ ∞0.6000 1.61869 13 ∞ ∞ 0.0000 1.00000 The 3rd surface Y toroidal surfaceThe 4th surface Y toroidal surface coefficient κ_(y) = −1.0031E+00A_(y4) = −1.7374E−02 The 8th surface aspheric surface coefficient κ =−1.0000E−01 A₄ = 1.5493E−04 A₆ = 3.0252E−07 The 10th surface asphericsurface coefficient κ = −5.4726E−01 A₄ = 3.7831E−04 A₆ = −1.8413E−03 A₈= 6.4043E−04 A₁₀ = −9.8987E−05 A₁₂ = −1.1518E−06 A₁₄ = −7.9320E−07Optical path difference function (Coefficient of optical path differencefunction: reference wavelength 422 nm, diffraction order 8th-order (407nm)) C₂ = −7.7249E−04 C₄ = −2.0466E−04 C₆ = −8.5677E−05 C₈ = 2.6999E−05C₁₀ = −4.1167E−06 The 11th surface aspheric surface coefficient κ =−3.3066E+02 A₄ = −3.7387E−03 A₆ = 8.8025E−03 A₈ = −5.2282E−03 A₁₀ =1.4815E−03 A₁₂ = −2.1825E−04 A₁₄ = 1.3236E−05

$\begin{matrix}{{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = \left( {R_{y} - \frac{X^{2}}{R_{x}\left( {1 + \sqrt{\left. {1 - {\left( {1 + \kappa_{x}} \right){X^{2}/R_{x}^{2}}}} \right)}} \right.} + {\sum{A_{xi}X^{i}}}} \right)} & \left\lbrack {{Math}\text{-}2} \right\rbrack \\{{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = \left( {R_{y} - \frac{X^{2}}{\left( {1 + \sqrt{\left. {1 - {X^{2}/R_{x}^{2}}} \right)}} \right.}} \right)} & \left\lbrack {{Math}\text{-}4} \right\rbrack\end{matrix}$

Herein, Z is a direction in the optical axis L direction (an advancingdirection of the light is positive), X, Y are a distance (height fromthe optical axis) in X, Y direction, R_(x) is a paraxial radius ofcurvature on XZ surface, R_(y) is a paraxial radius of curvature on YZsurface, and κ_(x) and A_(xi) are non-circular arc coefficients.

Further, in each of Examples, the outgoing surface (the 8th surface) ofthe coupling lens, the incident surface (the 10th surface) and theoutgoing surface (the 11th surface) of the objective lens are formedinto the aspheric surface axial symmetric around the optical axis L,which is regulated by an equation in which coefficients in Tables 9-13are substituted into the Math-5.

Further, on the incident surface (the 10th surface) of the objectivelens, furthermore, the diffraction ring-shaped zone around the opticalaxis is formed, and the pitch of the diffraction ring-shaped zone isregulated by an equation in which coefficients shown in Tables 9-13 aresubstituted into the optical path difference function of Math-6.

As shown in Tables 9-13, in the structure of Examples 7-13, thetemperature characteristic (the astigmatism amount generated at the timeof temperature rise of 30° C.) is within the range from −0.002 λrms to0.000 λrms, it can be seen that the astigmatism at the temperaturechange is sufficiently suppressed, however, as in Example 7, a value ofthe tetraphyllous aberration (4thAS) when both of the incident surfaceand outgoing surface of the beam-shper are structured by the cylindricalsurface is 0.009 λrms, in contrast to this, as in Examples 8-11, a valueof the tetraphyllous aberration (4thAS) when both of the incidentsurface and outgoing surface are structured by the toroidal surface is avalue not larger than 0.007 λrms.

As described above, as in Example 7, when both surfaces of theplastic-made beam-shaper are structured by the cylindrical surface, theastigmatism at the time of temperature change can be suppressed to thedegree of practically no-hindrance, however, it can be seen that, as inExamples 8-11, when the optical surface of the beam-szhaper arestructured by the toroidal surface, not only the astigmatism at the timeof temperature change, but also the suppression of the remainedaberration (4thAS (tetraphylluos aberration)) becomes possible, and thebetter optical characteristic can be obtained.

EFFECT OF THE INVENTION

According to the present invention, a plastic-made beam shaping lens,light source apparatus and an optical pick-up apparatus, by which adivergent beam whose cross sectional shape is an almost circle, can beprojected while the generation of the astigmatism following a change ofthe environmental temperature is suppressed, are obtained.

1. A light source apparatus comprising: a light source by which a light flux whose emitting angle is different in a horizontal direction and in a vertical direction is projected, and a beam shaping element, for converting the light flux into a light flux whose emitting angle is almost equal in both the horizontal direction and the vertical direction and projecting, of a single lens formed of plastic in which a linear expansion coefficient α_(n) satisfies the following expression (1) 5.0×10⁻⁵<α_(n)<8.0×10⁻⁵  (1), and a part of the beam shaping element is fixed and arranged to the light source, so that an astigmatism generated following the refractive index change of the beam shaping element generated by a temperature change is suppressed by an interval change, which is generated by the linear expansion of the beam shaping element, between the light source and the incident surface of the beam shaping element, wherein, in the beam shaping element, an outgoing surface is fixed so that a distance in the optical axis direction from the beam shaping element to the light source is almost constant in a range of the temperature change, wherein the beam shaping element is structured so that the astigmatism generated by the temperature change is suppressed by using the astigmatism generated following a shape change due to the temperature change of the beam shaping element, wherein a fixing member for fixing the beam shaping element outgoing surface is formed of a material having a linear expansion coefficient satisfying 10×10⁻⁵<α_(n)<3.0×10⁻⁵, wherein, in the beam shaping element, a cross sectional shape in the horizontal direction or in the vertical direction of at least one optical surface of the incident surface and the outgoing surface is a non-circular arc, wherein the surface shape of the beam shaping element incident surface satisfies the following Math-1 or Math-2, $\begin{matrix} {{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{R_{y}\left( {1 + \sqrt{\left. {1 - {\left( {1 + k_{y}} \right){Y^{2}/R_{y}^{2}}}} \right)}} \right.} + {\sum\limits_{i}{A_{yi}Y^{i}}}} \right)^{2}} & \left\lbrack {{Math}\text{-}1} \right\rbrack \\ {{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = \left( {R_{y} - \frac{X^{2}}{R_{x}\left( {1 + \sqrt{\left. {1 - {\left( {1 + k_{x}} \right){X^{2}/R_{x}^{2}}}} \right)}} \right.} + {\sum{A_{xi}X^{i}}}} \right)} & \left\lbrack {{Math}\text{-}2} \right\rbrack \end{matrix}$ wherein: Z is a distance in a Z-axis direction, Z corresponds to the optical axis direction, and Z is positive in an advancing direction of the light emitted by the light source, X and Y are distances in an X-axis direction, which corresponds to the horizontal direction, and a Y-axis direction, which corresponds to the vertical direction, the X and Y distances indicate a height from the optical axis in each of the X- and Y-axes, R_(x) is a paraxial radius of curvature on the XZ surface, R_(y) is a paraxial radius of curvature on YZ surface, and k_(x), k_(y), A_(xi), and A_(yi) are non circular arc coefficients.
 2. A light source apparatus of claim 1, wherein the surface shape of the beam shaping element outgoing surface satisfies the following Math-3 or Math-4, $\begin{matrix} {{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{\left( {1 + \sqrt{1 - {Y^{2}/R_{y}^{2}}}} \right)}} \right)} & \left\lbrack {{Math}\text{-}3} \right\rbrack \\ {{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = {\left( {R_{y} - \frac{X^{2}}{\left( {1 + \sqrt{1 - {X^{2}/R_{x}^{2}}}} \right)}} \right).}} & \left\lbrack {{Math}\text{-}4} \right\rbrack \end{matrix}$
 3. An optical pick-up apparatus comprising: the light source apparatus of claim 2, and a light converging element for converging the light flux on an information recording surface of an optical information recording medium, and reproducing and recording of information is conducted on the optical information recording medium.
 4. An optical pick-up apparatus of claim 3, further comprising: a divergent angle converting element for converting a divergent angle of the light flux projected from the beam shaping element outgoing surface, wherein the optical pick-up apparatus is structured so as to satisfy the following relational expression, 0.5<(L/S)×fc<1.0 wherein L is thickness on axis (mm) of the beam shaping element, S is distance (mm) on the optical axis between light source and the beam shaping element incident surface, and fc is focal distance (mm) of the divergent angle converting element.
 5. An optical pick-up apparatus of claim 4, wherein the divergent angle converting element is a coupling lens for converting the light flux projected from the beam shaping element into a parallel light parallel to the optical axis.
 6. A light source apparatus comprising: a light source by which a light flux whose emitting angle is different in a horizontal direction and in a vertical direction is projected, and a beam shaping element, for converting the light flux into a light flux whose emitting angle is almost equal in both the horizontal direction and the vertical direction and projecting of a single lens formed of plastic in which a linear expansion coefficient α_(n) satisfies the following expression (1) 5.0×10⁻⁵<α_(n)<8.0×10⁻⁵  (1), and a part of the beam shaping element is fixed and arranged to the light source, so that an astigmatism generated following the refractive index change of the beam shaping element generated by a temperature change is suppressed by an interval change, which is generated by the linear expansion of the beam shaping element, between the light source and the incident surface of the beam shaping element, wherein the surface shape of the beam shaping element outgoing surface satisfies the following Math-1 or Math-2, $\begin{matrix} {{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \begin{pmatrix} {R_{x} - \frac{Y^{2}}{R_{y}\;\left( {1 + \sqrt{\frac{1 - {\left( {1 + k_{y}} \right)\mspace{11mu} Y^{2}}}{R_{y}^{2}}}} \right)} +} \\ {\sum\limits_{i}\;{A_{yi}Y^{i}}} \end{pmatrix}^{2}} & \left\lbrack {{Math}\text{-}1} \right\rbrack \\ {{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = \begin{pmatrix} {R_{y} - \frac{X^{2}}{R_{x}\;\left( {1 + \sqrt{\frac{1 - {\left( {1 + k_{x}} \right)\mspace{11mu} X^{2}}}{R_{x}^{2}}}} \right)} +} \\ {\sum\;{A_{xi}X^{i}}} \end{pmatrix}} & \left\lbrack {{Math}\text{-}2} \right\rbrack \end{matrix}$ wherein: Z is a distance in a Z-axis direction, corresponds to the optical axis direction, and is positive in an advancing direction of the light emitted by the light source, X and Y are distances in an X-axis direction, which corresponds to the horizontal direction, and a Y-axis direction, which corresponds to the vertical direction, the X and Y distances indicate a height from the optical axis in each of the X- and Y-axes, R_(x) is a paraxial radius of curvature on the XZ surface, R_(y) is a paraxial radius of curvature on YZ surface, and k_(x), k_(y), A_(xi), and A_(yi) are noncircular arc coefficients.
 7. A light source apparatus of claim 6, wherein the surface shape of the beam shaping element incident surface satisfies the following Math-3 or Math-4, $\begin{matrix} {{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{\left( {1 + \sqrt{1 - {Y^{2}/R_{y}^{2}}}} \right)}} \right)} & \left\lbrack {{Math}\text{-}3} \right\rbrack \\ {{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = {\left( {R_{y} - \frac{X^{2}}{\left( {1 + \sqrt{1 - {X^{2}/R_{x}^{2}}}} \right)}} \right).}} & \left\lbrack {{Math}\text{-}4} \right\rbrack \end{matrix}$
 8. An optical pick-up apparatus comprising: the light source apparatus of claim 7 and a light converging element for converging the light flux on an information recording surface of an optical information recording medium, and reproducing and recording of information is conducted on the optical information recording medium.
 9. An optical pick-up apparatus of claim 8, further comprising: a divergent angle converting element for converting a divergent angle of the light flux projected from the beam shaping element outgoing surface, wherein the optical pick-up apparatus is structured so as to satisfy the following relational expression, 1.5<(L/S)×fc<1.0 wherein, L is thickness on axis (mm) of the beam shaping element, S is distance (mm) on the optical axis between light source and the beam shaping element incident surface, and fc is focal distance (mm) of the divergent angle converting element.
 10. An optical pick-up apparatus of claim 9, wherein the divergent angle converting element is a coupling lens for converting the light flux projected from the beam shaping element into a parallel light parallel to the optical axis.
 11. A light source apparatus comprising: a light source by which a light flux whose emitting angle is different in a horizontal direction and in a vertical direction is projected, and a beam shaping element, for converting the light flux into a light flux whose emitting angle is almost equal in both the horizontal direction and the vertical direction and projecting of a single lens formed of plastic in which a linear expansion coefficient α_(n) satisfies the following expression (1) 5.0×10⁻⁵<α_(n)<8.0×10⁻⁵  (1), and a part of the beam shaping element is fixed and arranged to the light source, so that an astigmatism generated following the refractive index change of the beam shaping element generated by a temperature change is suppressed by an interval change, which is generated by the linear expansion of the beam shaping element, between the light source and the incident surface of the beam shaping element, wherein, in the beam shaping element, a cross sectional shape in the horizontal direction or in the vertical direction of the least one optical surface of the incident surface and the outgoing surface is a non-circular arc, wherein the surface shape of the beam shaping element incident surface satisfies the following Math-1 or Math-2, $\begin{matrix} {{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \begin{pmatrix} {R_{x} - \frac{Y^{2}}{R_{y}\;\left( {1 + \sqrt{\frac{1 - {\left( {1 + k_{y}} \right)\mspace{11mu} Y^{2}}}{R_{y}^{2}}}} \right)} +} \\ {\sum\limits_{i}\;{A_{yi}Y^{i}}} \end{pmatrix}^{2}} & \left\lbrack {{Math}\text{-}1} \right\rbrack \\ {{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = \begin{pmatrix} {R_{y} - \frac{X^{2}}{R_{x}\;\left( {1 + \sqrt{\frac{1 - {\left( {1 + k_{x}} \right)\mspace{11mu} X^{2}}}{R_{x}^{2}}}} \right)} +} \\ {\sum\;{A_{xi}X^{i}}} \end{pmatrix}} & \left\lbrack {{Math}\text{-}2} \right\rbrack \end{matrix}$ wherein: Z is a distance in a Z-axis direction, corresponds to the optical axis direction, and is positive in an advancing direction of the light emitted by the light source, X and Y are distances in an X-axis direction, which corresponds to the horizontal direction, and a Y-axis direction, which corresponds to the vertical direction, the X and Y distances indicate a height from the optical axis in each of the X- and Y-axes, R_(x) is a paraxial radius of curvature on the XZ surface, R_(y) is a paraxial radius of curvature on YZ surface, and k_(x), k_(y), A_(xi), and A_(yi) are non circular arc coefficients.
 12. A light source apparatus of claim 11, wherein the surface shape of the beam shaping element outgoing surface satisfies the following Math-3 or Math-4, $\begin{matrix} {{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{\left( {1 + \sqrt{1 - {Y^{2}/R_{y}^{2}}}} \right)}} \right)} & \left\lbrack {{Math}\text{-}3} \right\rbrack \\ {{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = {\left( {R_{y} - \frac{X^{2}}{\left( {1 + \sqrt{1 - {X^{2}/R_{x}^{2}}}} \right)}} \right).}} & \left\lbrack {{Math}\text{-}4} \right\rbrack \end{matrix}$
 13. A light source apparatus comprising: a light source by which a light flux whose emitting angle is different in a horizontal direction and in a vertical direction is projected, and a beam shaping element, for converting the light flux into a light flux whose emitting angle is almost equal in both the horizontal direction and the vertical direction and projecting of a single lens formed of plastic in which a linear expansion coefficient α_(n) satisfies the following expression (1) 5.0×10⁻⁵α_(n)<8.0×10⁻⁵  (1), and a part of the beam shaping element is fixed and arranged to the light source, so that an astigmatism generated following the refractive index change of the beam shaping element generated by a temperature change is suppressed by an interval change, which is generated by the linear expansion of the beam shaping element, between the light source and the incident surface of the beam shaping element, wherein, in the beam shaping element, a cross sectional shape in the horizontal direction or in the vertical direction of at least one optical surface of the incident surface and the outgoing surface is a non-circular arc, wherein the surface shape of the beam shaping element outgoing surface satisfies the following Math-1 or Math-2, $\begin{matrix} {{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \begin{pmatrix} {R_{x} - \frac{Y^{2}}{R_{y}\;\left( {1 + \sqrt{\frac{1 - {\left( {1 + k_{y}} \right)\mspace{11mu} Y^{2}}}{R_{y}^{2}}}} \right)} +} \\ {\sum\limits_{i}\;{A_{yi}Y^{i}}} \end{pmatrix}^{2}} & \left\lbrack {{Math}\text{-}1} \right\rbrack \\ {{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = \begin{pmatrix} {R_{y} - \frac{X^{2}}{R_{x}\;\left( {1 + \sqrt{\frac{1 - {\left( {1 + k_{x}} \right)\mspace{11mu} X^{2}}}{R_{x}^{2}}}} \right)} +} \\ {\sum\;{A_{xi}X^{i}}} \end{pmatrix}} & \left\lbrack {{Math}\text{-}2} \right\rbrack \end{matrix}$ wherein: Z is a distance in a Z-axis direction, corresponds to the optical axis direction, and is positive in an advancing direction of the light emitted by the light source, X and Y are distances in an X-axis direction, which corresponds to the horizontal direction, and a Y-axis direction, which corresponds to the vertical direction, the X and Y distances indicate a height from the optical axis in each of the X- and Y-axes, R_(x) is a paraxial radius of curvature on the XZ surface, R_(y) is a paraxial radius of curvature on YZ surface, and k_(x), k_(y), A_(xi) and A_(yi) are non circular arc coefficients.
 14. A light source apparatus of claim 13, wherein the surface shape of the beam shaping element incident surface satisfies the following Math-3 or Math-4, $\begin{matrix} {{\left( {Z - R_{x}} \right)^{2} + X^{2}} = \left( {R_{x} - \frac{Y^{2}}{\left( {1 + \sqrt{1 - {Y^{2}/R_{y}^{2}}}} \right)}} \right)} & \left\lbrack {{Math}\text{-}3} \right\rbrack \\ {{\left( {Z - R_{y}} \right)^{2} + Y^{2}} = {\left( {R_{y} - \frac{X^{2}}{\left( {1 + \sqrt{1 - {X^{2}/R_{x}^{2}}}} \right)}} \right).}} & \left\lbrack {{Math}\text{-}4} \right\rbrack \end{matrix}$
 15. An optical pick-up apparatus comprising: a light source apparatus comprising: a light source by which a light flux whose emitting angle is different in a horizontal direction and in a vertical direction is projected, and a beam shaping element, for converting the light flux into a light flux whose emitting angle is almost equal in both the horizontal direction and the vertical direction and projecting, of a single lens formed of plastic in which a linear expansion coefficient α_(n) satisfies the following expression (1) 5.0×10⁻⁵<α_(n)<8.0×10⁻⁵  (1), and a part of the beam shaping element is fixed and arranged to the light source, so that an astigmatism generated following the refractive index change of the beam shaping element generated by a temperature change is suppressed by an interval change, which is generated by the linear expansion of the beam shaping element, between the light source and the incident surface of the beam shaping element, and a light converging element for converging the light flux on an information recording surface of an optical information recording medium, and the reproducing and/or recording of the information is conducted on the optical information recording medium, and further comprising: a divergent angle converting element for converting a divergent angle of the light flux projected from the beam shaping element outgoing surface, wherein the optical pick-up apparatus is structured so as to satisfy the following relational expression, 3.5<(L/S)×fc<1.0 wherein, L is thickness on axis (mm) of the beam shaping element, S is distance (mm) on the optical axis between the light source and the beam shaping element incident surface, and fc is focal distance (mm) of the divergent angle converting element.
 16. An optical pick-up apparatus of claim 15, wherein the divergent angle converting element is a coupling lens for converting the light flux projected from the beam shaping element into a parallel light parallel to the optical axis. 